Light sources, such as light emitting diodes and the like, and light conductors, such as optical fibers and waveguides, are used in a variety of applications. For example, in a fiber optic rotation sensor, which is arranged to sense rotation about an axis, an optical fiber is looped into a coil. Such a fiber optic rotation sensor ordinarily comprises an interferometer which includes a light source, a beam splitter, a detector, and a light path. The light path is provided by the coil, and the fiber optic rotation sensor is mounted on a rotatable platform. Light from the light source is conducted, usually by an optical fiber, to the beam splitter where the light is split into two beams which are directed to opposite ends of the light path and which then counterpropagate around that path. The light beams exit the light path, the light beams are recombined, and the resulting combined light beam is sensed by a detector. A sensing circuit connected to the detector determines any phase difference between the counterpropagating light beams.
Assuming that this fiber optic rotation sensor experiences no rotation, ideally no difference in phase between the counterpropagating light beams will be detected. On the other hand, if the sensor experiences rotation, there will be a phase difference between the counterpropagating light beams which can be detected to indicate the extent and direction of rotation.
Typically, a light emitting diode is provided as the source of light. The light emitting diode is coupled by a corresponding light coupler to the optical fiber which conducts the light emanating from the light emitting diode to the beam splitter. The light coupler is designed to ensure that light from the light emitting diode is coupled to the optical fiber with a high coupling ratio. The coupling ratio of a light coupler is determined by dividing the light received by the optical fiber by the light emanating from the light emitting diode. A light coupler having a high coupling ratio minimizes the coupling loss between the light emitting diode and the optical fiber.
A typical light coupler includes a housing for mounting the light emitting diode, a lens, and an end of the optical fiber together in such a fashion that the lens focuses light from the light emitting diode onto the end of the optical fiber. In order for a light coupler to achieve a high coupling ratio, the optical fiber must be precisely positioned at the focal point of the light emanating from the light emitting diode and focused by the lens.
In this type of light coupler, the diameter of the focus of the light emanating from the light emitting diode and the diameter of the core of the optical fiber typically are each approximately 0.0002 inch. With these dimensions, a 0.00002 inch (20.times.10.sup.-6 inch) positioning error between the focus of the light emanating from the light emitting diode and the core of the optical fiber can cause a 10% loss in the coupled power.
Prior art methods of aligning the focus of the light emanating from a light emitting diode and the core of the optical fiber have been able to routinely accomplish alignment within a 0.00002 inch tolerance or better. Once aligned, the light emitting diode, the lens, and the light receiving end of the optical fiber are secured in an effort to achieve alignment stability, i.e. to maintain this alignment during assembly and over the operating conditions typically experienced by the light coupler. Many methods are known to secure the diode/lens/fiber assembly once alignment has been achieved. These methods typically rely upon a securing means such as a weld, solder, or a bonding agent (e.g. an adhesive) in order to attempt to achieve alignment stability.
However, such prior art securing means for securing the diode/lens/fiber assembly have not resulted in alignment stability. A strong and stiff securing means causes the assembly to shift as the securing means cures, and adjustment of the assembly once the strong and stiff securing means cures induces alignment instability and/or is uncontrollable. A weaker securing means cannot maintain alignment stability over time and environmental changes. Thus, even though prior art alignment methods have been able to achieve an adequate initial alignment, these alignment methods have been unable to maintain alignment stability.